1. Field of the Invention
This invention relates generally to the storage and retrieval of op-code signal groups in a data processing unit and, more particularly, to the storage and retrieval of op-code signal groups having error checking and correction signal groups associated therewith.
2. Background of the Invention
Referring to FIG. 1, the technique for the storage and retrieval of op-code signal groups in a data processing system 10, according to the prior art, is illustrated. A central processing unit 11 stores op-code signal groups in read-only-memory (ROM) unit 12. In addition to the op-code signal groups stored in the ROM unit 12, error checking a correct signal groups for each op-code signal group are stored in the ROM unit 12. All of the op-code signal groups are stored in the ROM unit 12 even though each set of op-code signal groups used to control the operation of a data processing unit may not include all combinations of op-code signal groups. The op-code signal groups and error checking and correction signal groups are stored in the ROM unit 12 at the time of fabrication. During operation of the central processing unit, when an op-code signal group is required, and the central processing unit 11 requires a particular signal group, the central processing unit 11 sends the address of the required op-code signal group to the memory unit 12. The memory unit 12, in response to address signal group, retrieves the op-code signal group identified by the address signal group. The retrieved op-code signal group is applied to the error checking and correction code unit 13. The error checking and correction unit 13 examines the op-code signal group and the associated error checking and correcting signal group. Based on this examination and depending upon the error checking and correcting procedure implemented by the data processing system 10, a single error in the retrieved signal groups can be corrected and a double error can be identified. When correction is possible, the error is corrected by the error checking and correction unit 13 and the corrected op-code signal group is transferred to the central processing unit 11.
For example, each set of op-code signal groups can be, in current data processing implementations, over 32,000 32-bit words. The number of used 32-bit words can be over 22,000 32-bit words and the number of unique op-code words can be over 17,000. When the error checking and correction signal groups are added, the memory requirements can be large. In addition, the use of the ROM unit to store the complete set of op-code words is relatively inflexible.
A need has therefore been felt for apparatus and an associated method having the feature that the storage and retrieval requirements for op-code signal groups can be more flexible while retaining the use of error checking and correction techniques in a data processing system. It would be another feature of the apparatus and associated method to provide a programmable non-volatile storage unit for storing the group of addresses in the ROM unit of the op-code signal groups that are currently being utilized by the data processing system. It would be a still further feature of the apparatus and associated method to provide error checking and correction procedures to the op-code signal address signal groups stored in the programmable, non-volatile memory. It would be a more particular feature of the apparatus and associated method to implement the programmable, non-volatile memory in FLASH technology. It would be a still further feature of the apparatus and related method to provide for a reduced signal group storage requirement.